Polishing of a wafer by means of CMP is conducted in such a way that the wafer is pressed against a rotating polishing pad with a predetermined pressure while rotating the wafer and feeding a mechano-chemical polishing agent between the polishing pad and the wafer. Here, the wafer is surrounded by a retainer ring with the reverse face side of the wafer supported by a carrier (back plate) so that the wafer is pressed against the polishing pad.
In a conventional wafer polisher, however, the reverse face of the wafer is in direct contact with the hard surface of the carrier to press the wafer, and accordingly there has been a drawback that the reverse face of the wafer is damaged. Additionally, the surface precision of the carrier is transcribed onto the wafer, and hence the surface of the carrier needs to be fabricated with a high precision.
Hence, in order to solve these problems the present applicant has proposed a wafer polisher in Japanese Patent No. 3085948 in which a protective sheet integrated with the retainer ring is provided underneath the carrier (back plate). In the wafer polisher, the reverse face of the wafer is pressed by an air layer through the protective sheet, so that the direct contact of the hard surface of the carrier with the reverse face of the wafer is prevented. In this way, the reverse face of the wafer is prevented from being damaged. Additionally, it has become unnecessary to fabricate the surface of the carrier (back plate) with high precision.
In this case, as shown in FIG. 6, the protective sheet 1 is attached to a retainer ring holder 3, which is disposed to surround the carrier 2, with the peripheral part of the protective sheet 1 adhered to the retainer ring holder 3, and the retainer ring 4 is attached underneath the protective sheet 1.
However, when the protective sheet 1 and the retainer ring 4 are attached as described above, it is necessary to match the thickness of the retainer ring 4 with the thickness of the wafer W (1 mm or less), so that there occurs a drawback that the thickness of the retainer ring 4 is made to be extremely thin and accordingly the strength and durability of the retainer ring 4 are degraded.
It is preferable that the protective sheet 1 is attached uniformly without causing wrinkles across the entire sheet; however, there has been a drawback that it is difficult to attach without causing wrinkles by the above-described way of attachment.
On the other hand, a finding is obtained to indicate that polishing is possible without necessarily fixing the protective sheet 1 onto the retainer ring 4, depending on the material, thickness and the like of the protective sheet 1.
The present invention has been achieved in consideration of the above circumstances, and takes as its object the provision of a wafer polisher that permits easy attachment of the protective sheet and can ensure the strength and durability of the retainer ring.